Thin, planar, and relatively large area light sources are needed in many applications. Because of low light transmission in typical active matrix liquid crystal displays (LCD), very thin and powerful backlights are required to preserve a thin profile and readability in high ambient lighting conditions. Incandescent lamps or LEDs create local bright or dim spots because of the nature of point light sources. Additionally, significant heat dissipation in incandescent lamps or LEDs restrict practical use to low output conditions. Electroluminescent lamps suffer from having relatively low brightness, and are therefore only suitable for low light display outputs.
Recent advances in photoluminescent technology have met the demand for a thin, lightweight, planar lamp having a substantially uniform and durable display. One such fluorescent lamp is described in U.S. patent application Ser. No. 09/796,334. The lamp comprises a pair of glass plates connected by a sidewall, thereby creating an open chamber which contains a gas and photoluminescent material. Electrodes are placed on the outside of the glass plates to create an electric field inside the chamber, which ionizes the gas and causes the photoluminescent material to emit visible light.
Current photoluminescent lamps allow transmission of light through only one glass plate. A reflective coating is provided on the interior of the bottom plate, to guide additional light through the top glass plate. The top electrode may be patterned as a grid on the exterior surface of the plate using a silver-based compound. Thus, the existence of the reflective coating on the bottom surface is in part necessary to counteract the light attenuation by the top electrode.
Because the reflective coating restricts the use of such current lamps to one-sided light output, there remains a need for a two-sided, thin, lightweight lamp with substantial and uniform physical integrity across the entire surface.